Java中File,byte[],Object間的轉換

一、有兩點需要注意：

    1、Object 對象必須是可序列化對象 。

    2、可序列化的 Object 對象都可以轉換爲一個磁盤文件；反過來則不一定成立，只有序列
         化文件纔可以轉換爲 Object 對象。

二、相關的轉換方法：

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package javaapplication2;

import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 *
 * @author Dao
 */
public class Main
{

  public static byte[] getBytesFromFile(File f)
  {
    if (f == null)
    {
      return null;
    }
    
    try
    {
      FileInputStream stream = new FileInputStream(f);
      ByteArrayOutputStream out = new ByteArrayOutputStream(1000);
      
      byte[] b = new byte[1000];
      int n;
      while ((n = stream.read(b)) != -1)
      {
        out.write(b, 0, n);
      }
      stream.close();
      out.close();
      
      return out.toByteArray();
    }
    catch (IOException e)
    {
      e.printStackTrace();
    }
    
    return null;
  }

  public static File getFileFromBytes(byte[] b, String outputFile)
  {
    BufferedOutputStream stream = null;
    File file = null;
    try
    {
      file = new File(outputFile);
      FileOutputStream fstream = new FileOutputStream(file);
      stream = new BufferedOutputStream(fstream);
      stream.write(b);
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
    finally
    {
      if (stream != null)
      {
        try
        {
          stream.close();
        }
        catch (IOException e1)
        {
          e1.printStackTrace();
        }
      }
    }
    return file;
  }

  public static Object getObjectFromBytes(byte[] objBytes) throws Exception
  {
    if (objBytes == null || objBytes.length == 0)
    {
      return null;
    }
    
    ByteArrayInputStream bi = new ByteArrayInputStream(objBytes);
    ObjectInputStream oi = new ObjectInputStream(bi);
    
    return oi.readObject();
  }

  public static byte[] getBytesFromObject(Serializable obj) throws Exception
  {
    if (obj == null)
    {
      return null;
    }
    
    ByteArrayOutputStream bo = new ByteArrayOutputStream();
    ObjectOutputStream oo = new ObjectOutputStream(bo);
    oo.writeObject(obj);
    
    return bo.toByteArray();
  }
}